System and method for transmission of combined data stream

ABSTRACT

An electrosurgical system is disclosed. The electrosurgical system includes an electrosurgical instrument configured to generate a first and second data streams and a transmission circuit configured to convert the first and second data streams into a pulsed transmission signal. The first signal property of the transmission signal is representative of the first data stream and the second signal property of the transmission signal is representative of the second data stream. The transmission circuit is further configured to process the transmission signal to decode the first signal property into the first data stream and the second signal property into the second data stream.

BACKGROUND

1. Technical Field

The present disclosure relates to electrosurgical apparatuses, systems and methods. More particularly, the present disclosure is directed to a system and method of transmitting data from an electrosurgical device to an electrosurgical generator, wherein the data includes a plurality of data streams.

2. Background of Related Art

Energy-based tissue treatment is well known in the art. Various types of energy (e.g., electrical, ultrasonic, microwave, cryogenic, heat, laser, etc.) are applied to tissue to achieve a desired result. Electrosurgery involves application of high radio frequency electrical current to a surgical site to cut, ablate, coagulate or seal tissue. In monopolar electrosurgery, a source or active electrode delivers radio frequency energy from the electrosurgical generator to the tissue and a return electrode carries the current back to the generator. In monopolar electrosurgery, the source electrode is typically part of the surgical instrument held by the surgeon and applied to the tissue to be treated. A patient return electrode is placed remotely from the active electrode to carry the current back to the generator.

Ablation is most commonly a monopolar procedure that is particularly useful in the field of cancer treatment, where one or more RF ablation needle electrodes (usually of elongated cylindrical geometry) are inserted into a living body. A typical form of such needle electrodes incorporates an insulated sheath from which an exposed (uninsulated) tip extends. When an RF energy is provided between the return electrode and the inserted ablation electrode, RF current flows from the needle electrode through the body. Typically, the current density is very high near the tip of the needle electrode, which tends to heat and destroy surrounding tissue.

In bipolar electrosurgery, one of the electrodes of the hand-held instrument functions as the active electrode and the other as the return electrode. The return electrode is placed in close proximity to the active electrode such that an electrical circuit is formed between the two electrodes (e.g., electrosurgical forceps). In this manner, the applied electrical current is limited to the body tissue positioned between the electrodes. When the electrodes are sufficiently separated from one another, the electrical circuit is open and thus inadvertent contact with body tissue with either of the separated electrodes does not cause current to flow.

To perform the above-described electrosurgical procedures, various types of electrosurgical devices having specific electrode configurations are used. Generally, these electrosurgical devices include a variety of input controls and are configured to communicate with an electrosurgical generator. However, conventional electrosurgical instruments and generators utilize complicated circuits and processes for transmitting and receiving data which greatly limits functionality of these devices.

SUMMARY

The present disclosure relates to a system and method for transmitting multiple data streams relating to an electrosurgical instrument via a single pulsed transmission signal. First and second data streams are encoded into a signal transmission signal and transmitted across an isolation barrier to a signal processor, wherein the frequency of the transmission signal is representative of the first data stream and the pulse width is representative of the second data stream. The signal processor includes circuitry configured to decode the transmission signal to obtain the first and second data stream. More particularly, the signal processor includes a pulse counter for measuring the number of pulses of the transmission signal and a pulse width converter for measuring the pulse width of the transmission signal to obtain the first and second data streams, respectively.

According to one aspect of the present disclosure, an electrosurgical system is disclosed. The electrosurgical system includes an electrosurgical instrument configured to generate a first and second data streams and a transmission circuit configured to convert the first and second data streams into a pulsed transmission signal. First signal property of the transmission signal is representative of the first data stream and second signal property of the transmission signal is representative of the second data stream. The transmission circuit is further configured to process the transmission signal to decode the first signal property into the first data stream and the second signal property into the second data stream.

The present disclosure also relates to a method for the transmission of data which includes the steps of generating a first and second data streams and converting the first and second data streams into a pulsed transmission signal, wherein a first signal property of the transmission signal is representative of the first data stream and a second signal property of the transmission signal is representative of the second data stream. The method also includes the step of processing the transmission signal to decode the first signal property into the first data stream and the second signal property into the second data stream.

According to another aspect of the present disclosure, a data transmission system is disclosed. The system includes a transmission circuit configured to convert the first and second data streams into a pulsed transmission signal. The first signal property of the transmission signal is representative of the first data stream and the second signal property of the transmission signal is representative of the second data stream. The transmission circuit is further configured to process the transmission signal to decode the first signal property into the first data stream and the second signal property into the second data stream.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present disclosure are described herein with reference to the drawings wherein:

FIG. 1 is a schematic block diagram of an electrosurgical system according to the present disclosure;

FIG. 2 is a schematic block diagram of a generator and a hand piece according to one embodiment of the present disclosure;

FIG. 3 is an schematic block diagram of a transmission circuit according to the present disclosure; and

FIG. 4 is a flow chart illustrating a method for transmission for combined data streams according to the present disclosure.

DETAILED DESCRIPTION

Particular embodiments of the present disclosure are described hereinbelow with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail.

FIG. 1 is a schematic illustration of an electrosurgical system according to one embodiment of the present disclosure. The system includes an electrosurgical instrument 2 having a hand piece 12 and one or more electrodes 4 for treating tissue of a patient P. The instrument 2 may be a monopolar or bipolar instrument including one or more active electrodes (e.g., electrosurgical cutting probe, ablation electrode(s), sealing forceps, etc.).

The hand piece 12 is connected to the generator 10 by a cable 18 which includes a plurality of wires for transmitting electrical energy, hereinafter a supply line. Electrosurgical RF energy is supplied to the instrument 2 by a generator 20 via the supply line, allowing the instrument 2 to coagulate, seal, ablate and/or otherwise treat tissue. During electrosurgery the energy is returned to the generator 20 through a return electrode (not specifically shown). In a monopolar system, the return electrode is a conductive pad attached to the patient. In a bipolar system, wherein the instrument 2 is a bipolar electrosurgical forceps having opposing jaw members which include the active electrode 4 and a return electrode (not specifically shown) disposed therein, electrosurgical energy is similarly returned through the return electrode.

The generator 20 includes input controls (e.g., buttons, activators, switches, touch screen, etc.) for controlling the generator 20. In addition, the generator 20 may include one or more display screens for providing the user with variety of output information (e.g., intensity settings, treatment complete indicators, etc.). The controls allow the user to adjust power of the RF energy, waveform, and other parameters to achieve the desired waveform suitable for a particular task (e.g., coagulating, tissue sealing, intensity setting, etc.).

FIG. 2 shows a schematic block diagram of the generator 20 and the hand piece 12. The generator 20 includes a controller 24, a high voltage DC power supply 27 (“HVPS”) and an RF output stage 28. The HVPS 27 is connected to a conventional AC source (e.g., electrical wall outlet) and provides high voltage DC power to an RF output stage 28 which then converts high voltage DC power into RF energy and delivers the RF energy to the active terminal 30. The energy is returned thereto via the return terminal 32.

In particular, the RF output stage 28 generates sinusoidal waveforms of high RF energy. The RF output stage 28 is configured to generate a plurality of waveforms having various duty cycles, peak voltages, crest factors, and other suitable parameters. Certain types of waveforms are suitable for specific electrosurgical modes. For instance, the RF output stage 28 generates a 100% duty cycle sinusoidal waveform in cut mode, which is best suited for ablating, fusing and dissecting tissue and a 1-25% duty cycle waveform in coagulation mode, which is best used for cauterizing tissue to stop bleeding.

The generator 20 may include a plurality of connectors to accommodate various types of electrosurgical instruments (e.g., monopolar instruments, electrosurgical forceps, etc.). Further, the generator 20 is configured to operate in a variety of modes such as ablation, monopolar and bipolar cutting coagulation, etc. It is envisioned that the generator 20 may include a switching mechanism (e.g., relays) to switch the supply of RF energy between the connectors, such that, for instance, when the instrument 2 is connected to the generator 20, only the monopolar plug receives RF energy.

The controller 24 includes a microprocessor 25 operably connected to a memory 26, which may be volatile type memory (e.g., RAM) and/or non-volatile type memory (e.g., flash media, disk media, etc.). The microprocessor 25 includes an output port that is operably connected to the HVPS 27 and/or RF output stage 28 allowing the microprocessor 25 to control the output of the generator 20 according to either open and/or closed control loop schemes. Those skilled in the art will appreciate that the microprocessor 25 may be substituted by any logic processor (e.g., control circuit) adapted to perform the calculations discussed herein.

A closed loop control scheme is a feedback control loop wherein sensor circuit 22, which may include a plurality of sensors measuring a variety of tissue and energy properties (e.g., tissue impedance, tissue temperature, output current and/or voltage, etc.), provides feedback to the controller 24. Such sensors are within the purview of those skilled in the art. The controller 24 then signals the HVPS 27 and/or RF output stage 28, which then adjust DC and/or RF power supply, respectively. The controller 24 also receives input signals from the input controls of the generator 20 or the instrument 2. The controller 24 utilizes the input signals to adjust power outputted by the generator 20 and/or performs other control functions thereon.

The hand piece 12 includes one or more input controls 30 (FIG. 2) to adjust certain operating parameters of the generator 20, sensors 32 and ID transmitter 33. Placing the input controls at the instrument 2 allows for easier and faster modification of RF energy parameters during the surgical procedure without requiring interaction with the generator 20. The controls 30 include a plurality of input devices (e.g., buttons, switches, etc.) for adjusting intensity of the electrosurgical energy and selecting the operating mode (e.g., cut, coagulation, blend). The controls 30 provide complementary and/or redundant controls for the generator 20 which may be used to adjust the intensity of the energy output by the generator, change the operating mode (e.g., cut, coagulate, blend). The controls 30 include a plurality of resistive elements coupled to the inputs so that the inputs correspond to specific resistances. This allows for fewer wires to be used within the controls 30 since different input signals (e.g., corresponding voltage) can be transmitted along a single wire by varying the resistance thereby varying the voltage of the control current. The controls 30 transmit control signals to the generator 20.

DC voltage is employed by the hand piece 12 to transmit input signals to the generator 20. The DC voltage may be supplied by a DC power source via a DC line of the cable 18. More specifically, a DC voltage source is used to transmit a control current which is used by the hand piece 12 to transmit input signals to the generator 10. Using DC voltage to transmit control signals is well known in the art and is described in commonly owned U.S. Pat. Nos. 3,699,967 and 3,801,800, both of which are hereby incorporated by reference in their entirety herein.

The sensor 32 may include temperature sensors, impedance sensors, etc. which are in electrical communication with the active electrode 4 and are configured to measure tissue and/or energy properties at the treatment site. During operation, the sensors 32 transmit sensor signals to the microprocessor 25 and/or sensor circuitry 22.

The ID transmitter 33 stores and transmits an n-bits unique integer which serves as an identifier for the hand piece 12. This allows the generator 20 to identify which hand piece 12 is transmitting the sensor and/or control signals. Identifying the hand piece 12 is particularly important in electrosurgical procedures utilizing multiple active electrodes, such as ablation procedures, wherein multiple electrodes are used to ablate a wide segment of tissue. During such procedures, it is desirable to monitor tissue and energy properties for each of the active electrodes 14. This allows the generator 20 to pair the sensor and control signals with the corresponding hand piece 12 based on the transmitted identifier.

A transmission circuit 34 connects the controls 30, the sensors 32 and ID transmitter 33 of the hand piece 12 to the microprocessor 25. The transmission circuit 34 is configured to combine multiple data streams into a single pulsed transmission signal. The pulsed transmission signal includes a stream of pulses, the frequency of which represents a first data stream. The first data stream may be a voltage signal representative of some quantity of interest. The width of pulses of the pulsed transmission signal represents a second data stream, which denotes a second quantity of interest. The first and second data streams could be continuous analog signal levels, a sequence of digital logic levels, and the like. The first data stream may be either control signals or the sensor signals transmitted by the controls 30 and sensors 32, respectively, and the second data stream may be the identifier signal transmitted by the ID transmitter 33.

The controls 30 and sensors 32 are connected to a voltage-to-frequency converter 36 and transmit the control and sensor signals, respectively, thereto. The control and sensor signals, e.g., first data stream, are voltage signals and are converted to corresponding frequency pulses at the V/F converter 36. The V/F converter 36 transmits the frequency pulses to a first monostable multivibrator 46, wherein upon receiving the frequency pulse, the first multivibrator 46 creates a first pulsed signal having a fixed pulse length as a function of the frequency pulse of the V/S converter 36.

The V/F converter 36 is also coupled to a clock 28 which generates a clock signal at a predetermined frequency, such as 1 MHz. In response to the 1 MHz clock signal, the V/F converter 36 also transmits the frequency pulses to a n-bit shift register 44. The n-bit shift register 44 is a parallel-in serial-out shift register which is configured to output either a “1” or a “0” in response to the clocked signal from the V/F converter 36. In particular, the shift register 44 outputs serial data and accepts parallel digital data as input, with each parallel data bit appearing at the output in succession. After each parallel data bit has appeared at the output, the sequence begins again.

The shift register 44 is configured to accept parallel inputs from a load bit 40 and the ID transmitter 33, which provides the identifier, e.g., second data stream, for the hand piece 12 thereto. The shift register 44 is connected to a monostable multivibrator 47 which outputs pulses based on the input from the shift register 44. If the shift register 44 outputs a logic high (e.g., “1”) the multivibrator 47 outputs a second pulsed signal having a pulse wider than the first pulsed signal of the V/F converter 36. If the shift register 44 outputs a “0” the multivibrator 47 does not create a second pulsed signal.

The first pulsed signal of the V/F converter 36 and the second pulsed signal passing through the multibirator 47 are “OR-ed” at a digital logic two-input NOR gate 48 and the longer of the two pulsed signals is output therethrough thereby forming the pulsed transmission signal. The NOR gate 48 combines the pulses of the first pulsed signal from the first multivibrator 46, which are of variable time period (e.g., frequency) but of fixed pulse width, with the pulses of the second pulsed signal from the second multivibrator 47 which are also of fixed width to generate a pulsed transmission signal. The transmission signal includes pulses of variable time period/frequency and variable pulse width.

More specifically, the first pulsed signal is combined with the second pulsed signal, from the first and second multivibrators 46, 47 respectively, at the NOR gate 48. The first pulsed signal drives one input of the NOR gate 48 and causes the output of the NOR gate to a logic low “e.g., “0”) state, regardless of the state of the second input of the NOR gate 48. If the shift register 44 causes the multivibrator 47 to output the second pulsed signal, which is thereafter is transmitted to a digital logic two-input NOR gate 48, the second pulse drives the second input of the NOR gate 48 and forces the output of the NOR gate 48 to a logic low (“0”) state as well, regardless of the state of the first input to the NOR gate driven by the V/F converter 36.

Values of the RC networks (e.g, V/F converter 36, shift register 44, etc.) connected to the multivibrators 46, 47 are set such that the length of the pulse created by the second multivibrator 47 is longer than the length of the pulse created by the first multivibrator 46. This allows for detection processing of the output pulses from the NOR gate 48 to distinguish between so called “short” and so called “long” pulses, and thus determine whether the bit from the shift register 44 is a logic low (“0”) due to a short pulse or a logic high (“1”) due to a longer pulse. The timing of the longer pulse is also set by the components of the RC network such that the maximum length of a long pulse is less than the minimum pulse period from the V/F converter 36 driving the first multivibrator 46.

The output of the NOR gate 48 is driven low (“0”) when the output of either of the multivibrators 46, 47 is logic high (“1”). If the first multivibrator creates a short output pulse, and the second multivibrator 47 creates no output pulse, the output of the NOR gate remains low (“0”) only for the duration of the short pulse from the first multivibrator 46. Since the output of the shift register 44 controls the pulse output of the second multivibrator 47, the length of the output pulse from the NOR gate 48, e.g., the pulsed transmission signal, corresponds to the logic state output of the shift register 44 driving the second multivibrator 47.

The pulsed transmission signal is passed through an isolation barrier 50 which connects a non-isolated portion 66 (e.g., generator 20) with an isolated portion 68 (e.g., hand piece 12). The isolation barrier 50 includes one or more optical couplers 60 on the non-isolated portion 66 and one or more corresponding optical couplers 62 on the isolated portion 68. The optical couplers 60, 62 transmit the pulsed transmission signal across a physical gap, thereby isolating the hand piece 12 from the generator 20. In addition to optical couplers 60, 62 or similar light emitting devices, the isolation barrier 50 includes converters, such as analog-to-digital, digital-to-analog, voltage-to-frequency and frequency-to-voltage converters. Power is provided to the isolated portion optical couplers via an isolated DC/DC converter 64. Those skilled in the art will understand that the isolated DC/DC converter 64 and the isolation barrier 50 are optional if isolation is not desired.

The pulsed transmission signal is then passed through the isolation barrier to a signal processor (e.g., field programmable gate array 52) at the non-isolated portion 66. The frequency or the time period represented by the pulsed transmission signal is variable from pulse to pulse. The detection of the value of interest in the pulsed transmission stream is accomplished by one of the following: measuring the interval of time between pulses to obtain the pulse time period or counting the number of pulses received over some fixed interval of time, to obtain the average frequency of the pulsed transmission signal and thereby decode the first data stream. The width of each pulse is measured simultaneously with the frequency of the pulses of the pulsed transmission to extract the successive value of each pulse and thereby form the second data stream.

The signal processor measures both the time period/frequency and width of the pulses of the pulsed transmission signal to detect the first and second data streams, respectively. The signal processor uses digital logic wherein one counter is used to measure the pulse period or frequency and a second counter is used to measure the pulse width of each individual pulse. Those skilled in the art will appreciate that various counting circuits may be used to perform the detection function of the signal processor.

More specifically, the FPGA 52 decodes the pulsed transmission signal to obtain voltage information (e.g., pulse counts per unit of time) representative of the first data stream (e.g., control or sensor signals) and pulse width information representative of the second data steam (e.g., ID information). In particular, the FPGA 52 includes a pulse width converter 54 which measures the width of pulses of the pulsed transmission signal and then converts the pulse width to the hand piece 12 ID information. The FPGA 52 also includes a pulse counter 56 which decodes sensor or control signals by counting the number of pulses of the signal (e.g., frequency thereof). The decoded information is thereafter transmitted to the microprocessor 25 wherein the microprocessor 25 takes corresponding actions (e.g., adjust power, output ID information, etc.).

In one embodiment, the counter 56 counts the pulse width to distinguish between low (“0”) and high (“1”) logic states. In another embodiment, the counter 56 can be expanded to multiple logic level depending on resolution thereof to represent multiple bits. In particular, the binary logic level discussed above encompasses two (e.g., 2^1) states, which is sufficient to represent two pulsed signals encoding two data streams. Using a higher logic level which encompasses four (e.g., 2^2) or more (e.g., 2^n) states allows to represent multiple pulsed signals encoding multiple data streams. For instance, four pulse width represented by “00” “01” “10” and “11” may be used to describe four pulse states representative of four data streams.

The non-isolated portion 66, namely the generator 20 provides a signal which synchronizes the loading of the data inputs to the shift register 44 with the edges of the pulses from the V/F converter 36 to control the output order of the shift register 44. Since the generator 20 controls the timing of the loading of the bits into the shift register 44, the generator 20 can extract the register bits from the width of the pulses in the second data stream in the same sequence as the bits are output from the shift register 44.

In another embodiment, loading of the inputs to the shift register 44 can be performed entirely by the isolated portion 68 thereby alleviating the need for a load signal from the generator 20 to synchronize the data. This further reduces the need for signals to cross the isolation barrier 50.

This may be accomplished by transmitting a so-called “preamble” signal in addition to the data bits for the data streams to allow data detection circuitry (e.g., FPGA 52) on the non-isolated portion 66 to synchronize with the data stream transmitted by the circuitry (e.g., the NOR gate 48) on the isolation portion 68. The preamble is a unique bit pattern of 1's and 0's that does not duplicate nay of the possible bit patterns that occur in the data streams. The preamble is generated by encoding the N beats of the second data stream into a larger number of M bits. Since not all 2^M bit patterns are required to transmit the 2^N possible combinations of the bits in the second data stream, a unique pattern of M bits can be used as the preamble data pattern as illustrated below:

Second data stream having 8 bits: 1 1 1 1 1 1 1 1 Second data stream encoded to 0 1 0 1 1 1 1 1 1 1 10 bits: Preamble data, 10 bits: 1 0 1 0 1 0 1 0 1 0 Transmitted data sequence, 20 bits: 1 0 1 0 1 0 1 0 1 0 0 1 0 1 1 1 1 1 1 1 The FPGA 22 which detects the second data stream can then synchronize to the second data stream by waiting until the preamble pattern is detected. Once the preamble pattern is detected, the remaining bits in the data stream represent the data bits for the second data stream.

FIG. 4 illustrates a method for transmission of the first and second data stream via a single pulsed transmission signal. In step 100, the first data stream, e.g. control and/or sensor signals, are converted to a frequency pulse by the V/F converter 36. The V/F converter 36 transmits the frequency pulse to the first multivibrator 46 in step 110. In step 120, the first multivibrator 46, in response to the frequency pulse generates the first pulsed signal.

In response to the clock 38, the V/F converter 36 also transmits the frequency pulse to the shift register 44. In step 130, the shift register 44 accepts the input of the frequency pulse and the ID data from the ID transmitter 33 and outputs either a logic high (“1”) or low (“0”). In step 140, the second multivibrator 47 is actuated if the shift register 44 outputs a logic high and in step 150, the second multivibrator 47 generates a second pulsed signal which is longer than the first pulsed signal. In embodiments, more than two data streams may be transmitted via a single transmission signal by using higher logic states as discussed above.

In step 160, the first and second pulsed signals are processed at the NOR gate 48, wherein the longer of the pulses is used to form the pulsed transmission signal. The transmission signal is sent to the FPGA 52 across the isolation barrier 50. In step 170, the pulse counter 56 counts the number of pulses of the transmission signal to obtain the frequency and/or time period thereof and convert the obtained value into the first data stream. In step 180, the pulse width converter 54 measures the width of the pulses of the transmission signals to obtain the second data stream. The first and second data streams are thereafter transmitted to the microprocessor 25 for further processing.

The present disclosure provides for a system and method of combining two data stream for transmission using a single signal across an isolation barrier. Utilizing a single transmission signal minimizes the circuit complexity and power requirements of the isolated portion since the number of optical couplers or other isolated signal transmission components are reduced.

While several embodiments of the disclosure have been shown in the drawings and/or discussed herein, it is not intended that the disclosure be limited thereto, as it is intended that the disclosure be as broad in scope as the art will allow and that the specification be read likewise. Therefore, the above description should not be construed as limiting, but merely as exemplifications of particular embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto. 

1. An electrosurgical system, comprising: an electro surgical instrument configured to generate first and second data streams; and a transmission circuit configured to convert the first and second data streams into a pulsed transmission signal, wherein a first signal property of the transmission signal being representative of the first data stream and a second signal property of the transmission signal being representative of the second data stream, the transmission circuit further configured to process the transmission signal to decode the first signal property into the first data stream and the second signal property into the second data stream, wherein the transmission circuit includes: a voltage-to-frequency converter to convert the first data stream into a corresponding first frequency pulse; a first multivibrator for outputting a first pulsed signal in response to the first frequency pulse; a shift register configured to accept as input the first frequency pulse and the second data stream and to output at least one of a high logic and a low logic signals; a second multivibrator configured to output a second pulsed signal if the shift register outputs the high logic signal; and a NOR gate configured to select one of the first and second pulsed signals to form the transmission signal.
 2. An electrosurgical system according to claim 1, wherein the electrosurgical instrument includes: input controls configured to generate control signals which control an electrosurgical generator; and sensors configured to measure at least one of an energy property and a tissue property and generate sensor signals representative thereof.
 3. An electrosurgical system according to claim 2, wherein the first data stream is selected from the group consisting of control signals and sensor signals.
 4. An electrosurgical system according to claim 2, wherein the second data stream is an identifier for the electrosurgical instrument.
 5. An electrosurgical system according to claim 1, wherein the first signal property is a frequency of the transmission signal.
 6. An electrosurgical system according to claim 5, wherein the transmission circuit includes: a pulse counter configured to measure the number of pulses of the transmission signal to determine the frequency thereof.
 7. An electro surgical system according to claim 1, wherein the second signal property is a pulse width of each of the pulses of the transmission signal.
 8. An electrosurgical system according to claim 7, wherein the transmission circuit includes: a pulse width converter configured to measure the width of each of the pulses of the transmission signal.
 9. A data transmission system comprising: a transmission circuit configured to convert a first data stream and a second data stream into a pulsed transmission signal, wherein a first signal property of the transmission signal being representative of the first data stream and a second signal property of the transmission signal being representative of the second data stream, the transmission circuit is further configured to process the transmission signal to decode the first signal property into the first data stream and the second signal property into the second data stream; and wherein the transmission circuit includes; a voltage-to-frequency converter to convert the first data stream into a corresponding first frequency pulse; a first multivibrator for outputting a first pulsed signal in response to the first frequency pulse; a shift register configured to accept as input the first frequency pulse and the second data stream and to output at least one of a high logic and a low logic signals; a second multivibrator configured to output a second pulsed signal if the shift register outputs the high logic signal; and a NOR gate configured to select one of the first and second pulsed signals to form the transmission signal.
 10. A data transmission system according to claim 9, wherein the first signal property is a frequency transmission signal and the second signal property is a pulse width of each of the pulses of the transmission signal.
 11. A data transmission system according to claim 10, wherein the transmission circuit includes: a signal processor configured to measure the width of each of the pulses of the transmission signal and number of pulses of the transmission signal to determine the frequency thereof. 